1. Field of the Invention
The present invention relates to an apparatus and method of estimating an arousal level of a vehicle driver by particularly monitoring lateral displacements of a vehicle.
2. Description of Background Arts
A technology for preventing car accidents caused by the decline of driver""s arousal level is one of most important developmental subjects of today from the view point of vehicle safety. In recent years, studies for detecting drowsiness or arousal level of vehicle drivers, developments of techniques for warning them against falling into drowsy state are vigorously undertaken. When driver""s arousal level descends, especially when a vehicle travels at high speeds, serious accidents may happen. Even if he or she does not fall into such drowsy state, drowsiness induces him or her to an absent-minded state which hinders a quick action for averting accidents, this also leading to accidents.
Japanese Patent Application Laid-open No. Toku-Kai-Hei 5-58192 discloses a technique in which so-called xe2x80x9cdozing at the wheelxe2x80x9d is detected based on low frequency components in displacement quantity of a vehicle. In this disclosure, displacement quantities such as steering angle, lateral displacement of a vehicle and the like are monitored consecutively and low frequency components in frequency spectrum of the displacement quantity are extracted. On the other hand, low frequency components in frequency spectrum of displacement quantity at normal operations are memorized as sample data beforehand. Then, the low frequency components after a specified time elapses from the start of the vehicle are compared with those sample data. If a difference between the low frequency components and the sample data exceeds a predetermined value, it is judged that the driver dozes at the wheel.
However, the sample data which are used for the judgment reference are ones collected under a certain traveling condition (weather, road surface conditions, time, degree of traffic jams, vehicle speed and others). If the traveling condition changes, the judgment whether or not the driver is in a dozing state is accompanied by errors. That is, this background art has a problem that, when the traveling condition changes largely, it is difficult to obtain a correct judgment as to whether or not the driver is in a dozing state.
The applicant of the present invention has already proposed a method of estimating arousal level to solve such a problem in Japanese Patent Application Laid-open No. Toku-Kai 2000-185575. According to the technique disclosed in this publication, quantities of displacement in a widthwise direction of the vehicle are detected consecutively and respective frequency component powers are obtained by applying frequency conversion to these quantities of displacement. Next, the frequency domain is divided into a low frequency domain and a high frequency domain and an integration A1 of the frequency components powers in the low frequency domain and an integration A2 of the frequency components powers in the high frequency domain are obtained respectively. Then, evaluation values are calculated using these integrations A1, A2 and an arousal level of a vehicle driver is judged based on the evaluation values.
It is an object of the present invention to provide an arousal level estimating apparatus capable of making an accurate judgment of driver""s arousal level.
To achieve the object, an arousal level estimating apparatus comprises a power calculating means for calculating a frequency component power by applying a frequency conversion method to a lateral displacement quantity detected successively, a first evaluation value calculating means for calculating a first evaluation value based on a sum of the frequency component power calculated by the power calculating means, a second evaluation value calculating means for calculating a maximum value of frequency component power in a specified frequency domain including a fluctuation frequency as a second evaluation value, an evaluation value calculating means for calculating an evaluation value from a ratio of the first evaluation value and the second evaluation value and a judging means for judging a driver""s arousal level based on the evaluation value.